Fibrosing mediastinitis causing unilateral recurrent laryngeal nerve dysfunction.

A 45-year-old healthy woman with no significant medical history presented with gradually worsening dysphonia and hoarseness.

Physical examination revealed flaccidity of the left vocal fold and loss of abduction and adduction.

Transbronchial biopsy showed a dense fibrohyaline tissue without any suspicious findings for malignancy.

Good response and long-term disease control was achieved with high-dose steroids followed by maintenance steroid and methotrexate therapy.

CT and MRI chest and neck evaluation (Fig. 1-3) demonstrated a soft-tissue attenuation, non-calcified and diffusely enhancing mass in the middle mediastinum extending:

- to the infracarinal space and the aortopulmonary window, affecting the left laryngeal recurrent nerve (that exits from the vagus at the level of the aortic arch, passes through the aortopulmonary window and ascends to the superior mediastinum to reach the tracheoesophageal groove)

- to the left carotid space surrounding the origin of the supra-aortic vessels, the left carotid artery and infiltrating the left jugular vein, affecting the course of the vagus nerve (that descends with the carotid artery sheath into the upper mediastinum).

No bronchial or other cervical/mediastinal vessel narrowing were noted.

The secondary anteromedially rotation of the left aryepiglottic cartilage and the related medial position of the posterior vocal cord margin were noted. (Fig. 2)

Cervical involvement was also confirmed by US Doppler. (Fig.4)

Fibrosing mediastinitis (FM), also called idiopathic mediastinal fibrosis or sclerosing mediastinitis, is a rare non-malignant and progressive acellular collagen and fibrous tissue invasive proliferative condition within the mediastinum.

FM typically affects patients between 13 and 65 years with a strong predilection for young females [1]

FM has two major subtypes:

-The granulomatous form: Related to tuberculosis and histoplasmosis infection and due to immune-mediated hypersensitivity reaction (in one-third of cases with histopathologic overlap with IgG4-related disease [2])

-The non-granulomatous form (idiopathic reaction to autoimmune syndromes, sarcoidosis, radiation and drugs such as methysergide) (3),frequently associated with other fibrosing conditions such as Riedel thyroiditis, retroperitoneal fibrosis, sclerosing cholangitis, orbital pseudotumour, etc. [4].

Histopathology shows paucicellular fibrous tissue containing patchy infiltrates of mononuclear cells. [5]

There are two main presentation forms:

-Focal (80%): Typically seen in granulomatous forms as a localised mass of soft-tissue attenuation, frequently with stippled or dense calcifications and usually located in paratracheal or subcarinal compartments of mediastinum or in pulmonary hilum.

-Diffuse (20%): Typically seen in non-granulomatous forms as a diffusely infiltrating, non-calcified soft-tissue mass affecting multiple mediastinal compartments.

Clinical symptoms depend upon the compression of the surrounding structures of the mediastinum (chest pain, cough, breathlessness, pneumonia, dysphagia, etc). Complications such as superior vena cava syndrome, pulmonary hypertension and massive haemoptysis have been described. [6,7,8]

CT is a useful modality to assess the extent and the severity of involvement and to evaluate lung parenchyma that can show regional or diffuse oligaemia (in cases of pulmonary arteries encasement) and congestion and oedema with septal and bronchial wall thickening (in cases of pulmonary veins encasement).

Signal intensity shown on MRI can be variable depending on the presence of calcification or dense fibrotic scars (hypointense both on T1 and T2-weighted images) and inflammatory activity (hypo-isointense on T1-weighted images and hyperintense on T2-weighted images related to muscle and with variable contrast enhancement) [2].

Ultrasound can be used to evaluate possible cervical vessels involvement as shown in our case.

Definitive diagnosis requires biopsy (preferred to fine needle aspiration cytology due to extensive areas of fibrosis) to exclude malignancy.

Prognosis depends mainly of structures involved. FM can have an unpredictable course with both exacerbation of symptoms and spontaneous remission being reported.

Treatment options include antifungal agents in cases of histoplasmosis-related fibrosis, corticosteroids and stents placement/palliative surgery to relieve oesophageal, airway and vascular. In cases of localised forms, surgery can be curative. [8]

Written informed patient consent for publication has been obtained.